Current shunts (DC shunts) are widely used in many applications to measure the device or system current for metering and control applications. Generally, a conventional DC shunt is a four terminal device that is constructed using special metal elements having a known resistance, RDC. The resistive elements are welded between two posts or terminals (power terminals) that are used to interconnect the shunt in line with the main system or device current. Two separate terminals are used to sense the current flow through the resistive elements. The current measurement is made by measuring the voltage across the sense terminals and dividing that by the shunt resistance, namely
      I          D      ⁢                          ⁢      C        =                    V                  D          ⁢                                          ⁢          C                            R                  D          ⁢                                          ⁢          C                      .  
In order to reduce the unwanted heating (I2R) loss, most DC shunts are fabricated using very low resistive elements. For example, standard 50 mV shunts are offered with current ratings in excess of 1000 A resulting in a shunt resistance of 50 micro-ohms. Due to the low resistive nature of DC shunts, they are normally calibrated to ensure accurate current measurement across the sense leads.
One of the selection criteria for the shunt resistive elements is the need to have a very low temperature coefficient to minimize resistance variations with temperature. The I2R loss causes the shunt temperature to rise, causing its resistance to change. A very low temperature coefficient material has minimal resistance variation with its temperature, thus requiring no adjustment for measured currents at any temperature.
In many applications, installing a DC shunt is not a straightforward task. For example, in flooded Lead-Acid batteries, the intercell connectors are welded on the battery posts and cannot be easily removed. If current sensing needs to be added for monitoring purposes, an existing intercell connector needs to be removed first before welding the replacement DC shunt. This is a labor-intensive process, especially if it is to be performed in the field. In addition, if the battery has more than two posts (more than one intercell connector), replacing only one intercell connector with a shunt will cause the currents between the shunt and the remaining intercell connector to be unequal due to the large mismatch in resistance. Finally, since batteries have variable post designs and distances between posts, a large number of custom shunts need to be developed to fit the various battery designs.
Thus, there is a need to overcome limitations of DC shunts. Further, there is a need for a universal current measuring apparatus that can measure the current of any conductive element link. Even further, there is a need for accurate current measurements for use with an activity-based battery monitor.